Motors and alternators are typically designed for high efficiency, high power density, and low cost. High power density in a motor or alternator may be achieved by operating at high rotational speed and therefore high electrical frequency. However, many applications require lower rotational speeds. A common solution to this is to use a gear reduction. Gear reduction reduces efficiency, adds complexity, adds weight, and adds space requirements. Additionally, gear reduction increases system costs and increases mechanical failure rates.
Additionally, if a high rotational speed is not desired, and gear reduction is undesirable, then a motor or alternator typically must have a large number of poles to provide a higher electrical frequency at a lower rotational speed. However, there is often a practical limit to the number of poles a particular motor or alternator can have, for example due to space limitations. Once the practical limit is reached, in order to achieve a desired power level the motor or alternator must be relatively large, and thus have a corresponding lower power density.
Moreover, existing multipole windings for alternators and electric motors typically require winding geometry and often complex winding machines in order to meet size and/or power needs. As the number of poles increases, the winding problem is typically made worse. Additionally, as pole count increases, coil losses also increase (for example, due to resistive effects in the copper wire or other material comprising the coil). However, greater numbers of poles have certain advantages, for example allowing a higher voltage constant per turn, providing higher torque density, and producing voltage at a higher frequency.
Most commonly, electric motors are of a radial flux type. To a far lesser extent, some electric motors are implemented as transverse flux machines and/or commutated flux machines. It is desirable to develop improved electric motor and/or alternator performance and/or configurability.